The processes of quenching of work currents and overload currents differ in the energy of the electric arc initiated in the chamber. In the space where the electric arc acts on the chamber elements made of gassing materials, there are generated gasses which are used to cool the electric arc by absorbing thermal energy from the arc column. The larger the thermal energy of the arc, the more intensive gassing in the chamber.
A design of a quenching chamber comprising gassing plates arranged parallel to each other and pressed to each other by springs fixed in the chamber is known from European patent description EP0959483. The arcing knife of the switch attached to the switch arm is inserted between these plates, the switch functioning together with the chamber. The insertion of the arcing knife causes that the gassing plates move away from each other. The space formed by the separation of the gassing plates is the arcing knife channel. An electric arc is generated in the arcing knife channel when the switch is being opened in work or in overload conditions. The electric arc channel spreads along the arcing knife channel. As a result of the thermal action of the electric arc on the surfaces of the gassing plates the ablation phenomenon occurs, which consists in gassing of surfaces made of gassing materials. The generated gases cool down the electric arc by absorbing thermal energy from the arc column. As a result of gassing, gas pressure in the arc channel grows. These gasses are ejected into the decompression part of the quenching chamber situated above the part in which the gassing plates are fixed, and then, through an outlet located over the decompression part of the quenching chamber, they are ejected outside the quenching chamber. The quantity of ejected gases is limited by using an element which closes the outlet from the chamber after the arcing knife moves out. The functioning of the chamber while work and overload currents are interrupted consists in cooling the electric arc using the ablation phenomenon amplified by pressing the gassing plates on the arc column.
An inconvenience of that solution is that the arc channel corresponds to the arcing knife channel, which means that the distance between the gassing surfaces and the axis of the electric arc column is dependent on the dimensions of the arcing knife, which causes that the maximum intensity of gassing of the gassing plates of the quenching chamber is not ensured, which results in a reduction in the switching parameters of the quenching chamber. The fact that the arcing knife channel corresponds to the arc channel leads to degradation of the arc channel walls caused by the arc burning always in the same channel. This makes the ablation conditions worse over the life of the chamber. In addition, if the chamber operates in overload conditions, when the arc energy is the greatest, the distance between the gassing plates can increase. This happens due to the pressure occurring inside the chamber, if the force acting on the plates, directly proportional to the pressure of the generated gasses, is larger than the force of the springs supporting the gassing plates.
Another inconvenience of that solution is the fact that in order to reduce the quantity of ionized gases ejected towards the burning arc during the opening of the switch, movable elements closing the chamber after the exit of the arcing knife are used. The moving elements can be blocked by dirt or deformation, which causes that they will not serve their purpose i.e. they will not reduce the quantity of ejected gasses, but they can also lead to the switch failure by blocking the entrance into the arcing knife channel and thus disabling the proper functioning of the apparatus.
The presented solution employs only the phenomenon of arc quenching by cooling the arc column with gases. The use of only the phenomenon of arc column cooling results in a reduction in the switching parameters of quenching chambers. For that reason, in order to increase the switching parameters of quenching chambers made of gassing materials, there is a need to use the electric arc lengthening and flattening effect in such chambers, which will improve the arc quenching efficiency and thereby the chamber operation efficiency and will increase the switching parameters of a quenching chamber with gassing plates.
A design of a quenching chamber with magnetic blow-out of the arc, comprising a blowout coil and insulating plates suitably shaped and fixed to form narrow gaps, is known from patent description DE 19518051. The essential feature of electric arc quenching in this case is an increased power reception from the arc resulting from its lengthening. The arc is forced to increase its length and to move in the chamber through a magnetic field caused by the breaking current. The right direction of winding of the blowout coil ensures that the created electromagnetic force will push the arc column from the arcing knife channel to the quenching chamber.